Raw materials selection

Lime, sand, lime, pumice, ash and cinder are the major raw materials commonly used in the manufacture of lime mortar.

Lime: All types of lime can be used to make mortar, although not all lime mortars can be used for different situations. The main types of lime, viz., coarse lime and hydraulic lime, produce mortars of different properties, the former being suitable only for limited purposes such as jointing and light masonry work, while being more useful in other cases. It is important that the lime used is free from impurities such as silica, iron oxide and especially gypsum.

Sand: The sand for making a strong and durable mortar must be of good quality, i.e., it must be clean and sharp grained. The recommended fineness modulus of sand for mortar is 2.00–3.00.

Sand is added to the lime for at least two purposes:

1. To avoid shrinkage and cracking of mortar on hardening, because lime used alone shrinks and cracks on hardening.
2. To increase the bulk of the mortar; this is essential to make it more economical.

When used in appropriate proportions, sand facilitates the hardening of the lime paste by yielding a porous structure and allowing the atmospheric carbon dioxide access to the inner lime.

Pozzolanic materials: These include a variety of lightweight materials like surkhi, cinder, pumice and ash, which have been found to increase the strength of mortars when used in place of sand or even along with sand.

Water: In general, water suitable for drinking purposes can be used in the preparation of mortar. The water must be essentially free from alkalies, acids and organic residues.

Sometimes, cement is also added in small quantities to lime mortars to enhance the strength and setting properties of mortar. Depending on the type of the aggregate used, lime mortars are further distinguished into lime–sand mortars, lime–surkhi mortars, lime–sand–surkhi mortars and so on.